1. Field of the Invention
The present invention relates to a latch assembly, and in particular to a latch with an adjustable backset.
2. The Prior Arts
“Backset” refers to the distance from the edge of the door to the center of the pre-drilled hole for the lock. Most tubular locks come in a single size: 60 mm or 70 mm backset. The user needs to know the backset dimension to purchase the lock. If the lock purchased by the user has a backset different from the hole drilled on the door, the lock is unusable. Thus, the lock has only a single backset dimension is restricted to be used on the door having the pre-drilled hole with the same backset dimension. Accordingly, a latch assembly with an adjustable backset has been developed. The latch assembly can change the assembly method of transmission members of the lock and the backset distance can be set to one of two predetermined distances. The latch assembly according to the present invention is more applicable than the conventional latch assembly.
China Patent No. 99248490.1 discloses a “Latch bolt mechanism of a tubular lock with adjustable backset by an extension casing”, which can be adjusted to provide two predetermined backset positions. The latch bolt mechanism includes a latch bolt housing, a plate assembly including a first plate and a second plate, an actuating plate, a follower plate located between the first plate and the second plate, and an extension casing mounted around an inner end of the plate assembly and movable longitudinally to the plate assembly. One end of the actuating plate includes a hook-shaped connecting member for retracting the latch bolt and the other end of the actuating plate includes an upper tooth and a lower tooth. The follower plate includes an upper tooth and a lower tooth, each of which includes a block formed thereon. When the spindle of the lockset is turned, one of the upper tooth and the lower tooth of the follower plate is pressed by a lateral side of the spindle. The follower plate presses the blocks of the actuating plate, and therefore the follower plate retracts the latch bolt. Moreover, the extension casing includes upper and lower slots in top and bottom sides thereof, respectively. The slots receive the blocks of the follower plate, respectively. Because the slots have a length longer than that of the blocks of the follower plate, the extension casing can drive the follower plate to move relative to the actuating plate and the extension casing can move relative to the follower plate, i.e. the extension casing and the follower plate can have different moving distance relative to the actuating plate. Thus, a latch of a tubular lock is adjusted to form two different backset dimensions by moving the extension casing. However, a disadvantage of this configuration is that this positioning mechanism of the latch bolt can not be adjusted accurately, because when the extension casing moves together with the follower plate between two backset dimensions, the relative moving space between the extension casing and the follower plate is realized by the slots of the extension casing that have a length longer than that of the blocks of the follower plate, and there is no position fixing member for the two different backset dimensions.